The Department of Nuclear Medicine, in conjunction with the National Cancer Institute and the Department of Radiology, performs clinical research in the use of imaging in oncology. In particular, they are studying the use of positron emission tomogra-phy (PET) images, in conjunction with computer tomography (CT) and magnetic resonance (MR) images, to evaluate the effects of therapy on tumors. Several therapeutic agents are being studied, among them various anti-angiogenesis therapies. The PET scanners are used to measure glucose metabolism, blood flow, and blood volume in tumors over the course of therapy. CT scans are used to determine tumor morphology, and MR imaging is used to determine both morphology and parameters related to tumor perfusion. This research is geared toward developing, implementing, and testing methods to better quantify the data obtained from the images and to determine if these methods are efficacious for the monitoring of tumor therapy. These methods involve determination of tumor morph-ology as well as the optimal determination of functional parameters such as blood flow, metabolism, and blood volume. The overall goal is development of a clinically useful meth-odology for determining tumor response to therapy at an earlier phase of therapy than is currently possible. Such a methodology could permit optimal adjustment of the course of therapy while it is still proceeding, potentially improving both tumor response and patient morbidity. Several areas of investigation are being pursued toward achieving this goal. 1. Development of new reconstruction techniques to improve noise properties of the image sets. This noise reduction will both improve the ability of the physician to visually interpret the images and improve the noise in quantitative parameters derived from the images. ISP: Nuclear Medicine Department 2. Assessment of the physiologic models employed for blood flow measurement, using O-15 water. Several models are being analyzed, especially their utility in producing functional flow images. The results of these PET flow models are also being compared to similar data obtained from Gd-DTPA dynamic MR images. The variability and reproducibility of each of the methods is also being deter-mined, using replicate measurements. 3. Methods for making accurate, noninvasive measurement of the arterial input function are being assessed. These methods compare LV cavity and aorta derived arterial input functions with actual arterial sampling. Several schemes are being explored to correct for partial volume and spill in/out effects. 4. Methods for using three-dimensional region growing to more accurately assess tumor volume, metabolic volume, and perfused tumor volume are being explored. These methods will be employed to make objective assessments of the various physiologic parameters (e.g., fluorodeoxyglucose uptake), and receiver operat-ing characteristics analysis will be used to determine which of these quantitative indices is best for detecting disease, and to determine if quantitative measures are better than subjective visual assessment. Investigation of methods to reduce transmission scan time in PET imaging is studied. Transmission scan time is now a major limiting factor in the clinical application of PET to oncology whole body imaging. Watershed methods are being explored to segment very short attenuation scans, thus significantly reducing transmission scan time.